Radioactive (14C-) will be prepared by incorporation of labeled organic substances such as acetate into replacement, agitated, mycelial cultures, and cell-free extracts of Penicillium rubrum. Cultures will be assayed for the presence and properties of rubratoxin-synthesizing enzymes. Biological activity of the toxin will be determined through animal studies, bioassays with test fungi and algae, (especially RNA polymerase activity in vivo and binding of substrate molecules in vitro). Other studies will include the preparation of appropriate haptens and the evaluation of rubratoxin effects on complement, prothrombin time, T and B lymphocyte activity, and erythropoiesis.